Biotransformation of Cycloartane-Type Sapogenols, Cycloastragenol and Cyclocanthogenol, by Cunninghamella blakesleeana NRRL 1369

Cycloastragenol is a cycloartane-type sapogenol found in Astragalus species. It is a minor metabolite mainly present in the roots of the plant and possesses very interesting pharmacological activities [1, 2].

The biotransformation of cycloastragenol by the fungus Cunninghamella blakesleeana was investigated previously by our group [3]. Inspired by the diversity of the transformed products, further studies were carried out on cycloastragenol (CG) and another secondary metabolite, named cyclocanthogenol (SKG).

The biotransformation process was conducted in two scales; analytical scale and preparative scale. One-stage fermentation protocol was followed where the saponins were fed to the biotransformation media 72 hours after the inoculation. In the analytical scale, both submerged (30°C, 200 rpm) and surface (30°C) culture conditions were tested, taking 2 mL samples for 3 weeks for the evaluation of the chemical profiles, followed by preparative scale studies by using 500mg of SKG and 1000mg of CG. Incubation period was continued with centrifugation, extraction with ethyl acetate and n-butanol, and evaporation under vacuum. The isolation and purification studies performed on the extracts yielded total of 13 metabolites, 10 from CG and 3 from SKG. Structures of the isolated metabolites were elucidated by 1D- and 2D NMR techniques, and LC-MS analyses.

The major products obtained from each sapogenol Cb_CG_MF_01 and Cb_SKG_MF_01 have the same tetracyclic steroidal framework with a primary alcohol substitution at C-11 position, encountered for the first time in microbial transformation studies [3].

Acknowledgement: ARS Culture Collection, TUBITAK (108T654–109S345).

References: 1. Bedir E et al. (2000) Biol Pharm Bull 23: 834–837.

2. Valenzuela HF et al. (2009)J Immunol 182: 90.30.

3. Kuban M et al. (2010) Org Lett 12: 4252–4255.